CBSE Class 10 Biology Heredity and Evolution Notes Set 11

Origin of Life

1. Special creation: the belief that God created every species separately.
2. Spontaneous generation (abiogenesis): life arises from non-living matter. Redi and Pasteur disproved it and established biogenesis, that life comes only from life.
3. Chemical evolution (Oparin and Haldane): the early atmosphere had methane, ammonia, hydrogen and water vapour but no oxygen. Energy from lightning and ultraviolet light made simple organic molecules, which collected in the sea as a hot dilute soup and formed the first cells. The Urey–Miller experiment (1953) produced amino acids from these gases by electric sparks.

Evidence for Evolution

1. Homologous organs have a common structure but different functions (human arm, bat wing, whale flipper); analogous organs have the same function but different origin (bird and insect wings).
2. Vestigial organs are reduced remnants: appendix, wisdom teeth and the nictitating membrane in man, hind-limb bones in the python.
3. Connecting links: Archaeopteryx has features of reptiles (teeth, tail) and birds (feathers, wings).
4. Embryology: early embryos of vertebrates look alike.
5. Biochemistry: similar proteins and DNA in related species.
6. Fossils show the gradual change of forms through geological time.

Theories of Evolution

1. Lamarck: use and disuse of organs and inheritance of acquired characters. Weismann disproved it by cutting the tails of mice for several generations.
2. Darwin: natural selection. Organisms produce more offspring than survive; there is variation and a struggle for existence; the fittest survive and pass on their useful variations. Darwin was influenced by Malthus, who said that population grows geometrically but food only arithmetically.
3. De Vries' mutation theory: new species arise suddenly by large heritable changes (mutations).
4. Modern synthesis: variation from mutation and recombination, acted on by natural selection.

Population and Human Evolution

A population changes by natality (births) and immigration, which increase it, and mortality (deaths) and emigration, which decrease it. Humans and apes share a common ancestor; humans have a better developed brain and senses, an upright posture and a different jaw and teeth.